The Transitional Changes Between the Fluvial and Marine Environments as Indicated by Holocene Fauna in Siba at Basrah, Southern Iraq

The study is conducted at one point in Siba City, Basrah to describe its fauna content and texture. The current study attempts to reveal the transitional stage between marine and fluvial environments. Variation in sediment texture provides an index of environmental transformation in the Recent (Holocene Epoch). From grain size analysis, we notice an increase in the percentage of silt and a decrease in the percentage of sand in meters (1-3), a gradual increase in the percentage of sand and a gradual decrease in the percentage of silt in meters (4-6), and in meter 7 there is a high increase in sand and a high decrease in silt, and a gradual decrease in clay from meter 1 to meter 7, a decrease in the percentage of Total Organic Carbon (TOC) is also noted. Recent fauna reinforces sedimentary evidence that marine regression began at depths 5 and 7 m, marine species decrease significantly, and one of the most important marine groups is the Miliolina (Suborder) from foraminifera, where Triloculina, Quinqueloculina, and Spiroloculina are found; on the other hand, describe other groups; Nodosariina, Rotaliida, Textulariina, Polymorphinina and Nodosariina in addition to Ostracoda.